Davis pitched more innings resulting in a higher WAR (7.7 to 6.4), but essentially they were the same seasons. Their OBP-against those two years also were in line with each other, .277 for Davis, .273 for Soria. They both made the All Star game both seasons, so before their respective meltdowns they had each established a track record of excellence.
Davis, in fact, won the Cy Young award in 1989 with the Padres and when he signed with Kansas City on December 11, 1989 the Royals became the first team to possess both reigning CYA winners. (Bret Saberhagen won the AL award, but you knew that.) While the signing excited the fan base, it was also completely unnecessary. Jeff Montgomery saved 18 games with a 1.37 ERA in 1989 and was more than capable of handling the role. But this was the offseason of let's get Mr. Kauffman one more championship so Davis was brought in to close and Storm Davis was added to the rotation (a disaster of its own).
Opening day arrived and there was a fair amount of enthusiasm surrounding the team as they were one of the favorites in the West. But then Sam Horn happened and the team seemingly never recovered. For those not familiar with the reference I'll explain - in the bottom of the 8th inning left handed hitting Sam Horn came to the plate representing the tying run, but rather than bring in his shiny new left handed closer, manager John Wathan elected to let right-hander Steve Farr pitch to Horn. Horn homered and the Royals eventually lost the game in 11 innings.
It was a questionable decision in real time because back then a closer routinely entered the game before the 9th inning. Many still point to that at bat as the moment the franchise began its downward turn, that is of course nonsense but also hard to argue against. If the game had any effect on Davis though, it didn't immediately manifest itself. He only allowed 1 baserunner in his first 4 appearances and was 3/3 in saves. But then things started going south.
In a 5-1 loss to the Blue Jays on April 21st he gave up his first run when he walked 2 and gave up 2 hits in a single inning of work. The next day he walked 2 more and allowed 1 hit in a 7-1 win. On April 27th he blew his first save when he gave up 4 runs in the 9th inning. He blew 2 more saves the first week of May but then had a couple decent outings. He blew another save May 11th and two days later lost the closer job to Montgomery. Though Wathan said Davis and Montgomery would be flip flopped it never happened. Montgomery took the job all the way to the Royals Hall of Fame. When he was replaced in favor of Montogmery he had a 7.24 ERA and was 5/9 in save opportunities.
Davis rebounded a bit in middle relief (4.58 ERA) but was never trusted with the closers role again. Eventually they tried him in the rotation (like many are suggesting with Soria) but that worked out about as well as expected. Two years later he was traded to the Braves for Juan Berenguer bringing his Royals career to an end. The final damage was a 76 ERA+ in 167.2 innings and a hard lesson in the unpredictability of closers.
Soria has a 6.55 ERA and is 7/12 in opportunities. Today he was replaced by Aaron Crow, who could become the Montgomery to Soria's Davis. If Crow is successful it's hard to imagine him moving back to his setup role but it could happen I guess. Though Davis is a good comp at the moment I have to believe, that unlike Davis, Soria will eventually recover. And though he may never be an elite closer again, he'll at least be effective, especially if it turns out he he has been pitching with an injury.